EP0942430B1 - Method and apparatus for 1-T SRAM compatible memory - Google Patents
Method and apparatus for 1-T SRAM compatible memory Download PDFInfo
- Publication number
- EP0942430B1 EP0942430B1 EP99301728A EP99301728A EP0942430B1 EP 0942430 B1 EP0942430 B1 EP 0942430B1 EP 99301728 A EP99301728 A EP 99301728A EP 99301728 A EP99301728 A EP 99301728A EP 0942430 B1 EP0942430 B1 EP 0942430B1
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- EP
- European Patent Office
- Prior art keywords
- refresh
- memory
- memory array
- array
- cells
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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- 238000000034 method Methods 0.000 title claims description 10
- 230000004044 response Effects 0.000 claims description 9
- 230000000977 initiatory effect Effects 0.000 claims description 4
- 230000000737 periodic effect Effects 0.000 claims description 4
- 230000002401 inhibitory effect Effects 0.000 claims description 2
- 230000003111 delayed effect Effects 0.000 description 3
- 239000004065 semiconductor Substances 0.000 description 3
- 230000007704 transition Effects 0.000 description 3
- 230000004913 activation Effects 0.000 description 2
- 238000001514 detection method Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 230000006870 function Effects 0.000 description 2
- 230000008901 benefit Effects 0.000 description 1
- 239000000872 buffer Substances 0.000 description 1
- 239000003990 capacitor Substances 0.000 description 1
- 230000009849 deactivation Effects 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
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- 238000012986 modification Methods 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
- 230000011664 signaling Effects 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
- 230000001360 synchronised effect Effects 0.000 description 1
Images
Classifications
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
- G11C11/21—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements
- G11C11/34—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices
- G11C11/40—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices using transistors
- G11C11/401—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices using transistors forming cells needing refreshing or charge regeneration, i.e. dynamic cells
- G11C11/406—Management or control of the refreshing or charge-regeneration cycles
- G11C11/40615—Internal triggering or timing of refresh, e.g. hidden refresh, self refresh, pseudo-SRAMs
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
- G11C11/21—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements
- G11C11/34—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices
- G11C11/40—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices using transistors
- G11C11/401—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices using transistors forming cells needing refreshing or charge regeneration, i.e. dynamic cells
- G11C11/406—Management or control of the refreshing or charge-regeneration cycles
Definitions
- This invention relates to semiconductor memory.
- it relates to both SRAM and DRAM, and to using DRAM cells for building SRAM compatible memory.
- a conventional DRAM (dynamic random access memory) memory cell consisting of one transistor (“1-T”) and one capacitor is significantly smaller, in terms of chip surface area, and hence less expensive than an SRAM (static random access memory) cell which conventionally consists of 4 to 6 transistors.
- data stored in the DRAM cell requires periodic refresh, which is not required in the SRAM cell.
- Prior art for example "pseudo-SRAM” (see Toshiba Corp. Data Book, 1990) attempted to use DRAM cell for SRAM applications with little success, because the device required an external signal fr controlling memory refresh and during memory refresh, external access is delayed. As a result the refresh is not transparent and the device is inherently not compatible with any SRAM device.
- a method of operating a memory array having a plurality of memory cells that require period refreshing comprising the steps of: periodically generating refresh requests; initiating refresh cycles in response to the refresh requests only when external accesses to the memory array are not pending; inhibiting refresh cycles in response to the refresh requests when external accesses to the memory array are pending; accumulating refresh requests corresponding to inhibited refresh cycles; and initiating refresh cycles in response to accumulated refresh requests only when external accesses to the memory array are not pending.
- a memory system comprising an array of memory cells, each cell requiring periodic refreshing; an access controller coupled to the memory array for externally accessing the memory cells; a refresh controller coupled to the memory array for refreshing the memory cells; and wherein the refresh controller is arranged only to refresh the memory cells during an idle time between external accesses to the memory cells, wherein the refresh controller includes a refresh timer configured to periodically generate refresh signals, and a refresh accumulator configured to accumulate refresh signals provided by the refresh timer until associated refresh operations can be performed during the idle time between external accesses to the memory cells.
- the system may further comprise an arbiter coupled between the access controller and the refresh controller. Refreshes can be accumulated in an accumulator in the refresh controller until they can be performed during the idle time.
- the cells each include no more than one transistor.
- the cells may each be a DRAM cell and the memory array may have a peak operating frequency at least equal to a peak frequency of the external accesses.
- the memory array may be operated in response to a clock signal such that a memory cycle time of the memory array in equal to a period of the clock signal.
- the memory cell Since the method and system in accordance with this invention is preferably used with a single transistor memory cell which is essentially the same as a conventional DRAM cell, the memory cell requires periodic refresh.
- the refresh takes up memory bandwidth.
- the total bandwidth required by both the refresh and external access is smaller than or equal to the memory bandwidth afforded by the memory cell array, memory refresh can be satisfied with no impact (in terms of timing) on the external access.
- Refresh is a relatively infrequent event, so the average bandwidth that it occupies is relatively small compared to the peak bandwidth available to the memory array.
- the memory operating frequency is 100MHz, and the refresh frequency of 62.5KHz (for 1000 rows of memory cells and 16ms refresh time for each row) occupies only 0.0625% of the total available bandwidth.
- the refresh should have no impact on the external access.
- the cycle time of the memory array is 10ns
- each occurrence of refresh access takes 10ns and each external access takes at least 10ns.
- the external access time should take no less than 20ns (10ns for refresh and 10ns for actual access), or the external access frequency should be less than 50MHz.
- the average frequency of external access is in general smaller than the peak access frequency.
- a memory cell array contains 128K words of 32-bits.
- the array therefore has 32 data I/O lines.
- FIG. 1 shows an example of the present memory system with such an array. It includes the memory cell array 10, a memory array sequencer 14, a memory address multiplexer 16, a refresh controller 20, an external access controller 22 and an access arbiter 26.
- the memory array 10 is arranged into 2K rows and 2K columns. Associated with each column is a sense-amplifier in block 30 which performs the data sensing, restore and write operation. During each access, one cell array row is activated and the 2K memory cells of that row are connected to the sense-amplifiers 30 in each column.
- the sense-amplifiers 30 are conventionally connected to the I/O buffers 36 through a set of 2K-to-32 column multiplexers 38.
- the memory array sequencer 14 generates the conventional DRAM control signals RAS# and CAS# for controlling the operation of the array. Functions of the RAS# and CAS# signals are similar to those described in US Patent #5,615,169 to the same inventor, and incorporated by reference herein in its entirety.
- the external access controller 22 interprets external access commands and generates read/write requests. In one embodiment, two signals are used to determine an external access: Clock (CLK), and Address-Strobe (ADS#). The external access is detected at the rising clock edge on the activation of an Address-Strobe (ADS#) signal.
- FIG. 2 shows the timing relationship of these two signals.
- the ADS# and CLK signaling is similar to the industry standard for synchronous SRAM (See e.g. Pentium Processor 3.3v Pipelined BSRAM specification version 2.0 May 25, 1995, Intel).
- the external interface signal can be made similar to that of standard asynchronous SRAM (See Data sheet for M5M5178P, 64K SRAM, Mitsubishi Semiconductor Memory Data Book, 1990).
- the ADS# signal can be generated internally by an address transition detection circuit similar to the one described in "A 21-mW 4-Mb CMOS SRAM for Battery Operation” by Murakami et al., JSSC, Vol. 26, No. 11, pp. 1563-1567, November 1991.
- the ADS# signal thus generated can be used to synchronize the internal operation of the memory.
- the external-access controller 22 Upon the detection of an external access, the external-access controller 22 activates the request signal EREQ# to the access arbiter 26 which in turn drives the ASEL signal high to select an address on the External Access Address Bus ECAdd for the accessing address to the memory array 10.
- Arbiter 26 also activates the External Access EA# signal which is input to the memory array sequencer 14 for generating the RAS# and CAS# signals for controlling the array operations. The timing of these signals is also shown in FIG. 2.
- the access priority is always granted by arbiter 26 to the external access. By doing so, external accesses are not delayed by the refresh.
- This embodiment is configured to have the memory cycle time equal to a clock period, thus allowing a random access per clock cycle.
- the access is random, that is, it can be any address spanned by the device address space.
- the arbiter 26 evaluates the requests and drives the ASEL signal, input to the address multiplexer 16, to select one of the two addresses: refresh address RFAdd or external access address ECAdd to be used for the memory array 10 operation. Only in the absence of an external access does the arbiter 26 allow a refresh access to go through. In case of collisions, the refresh is delayed. The timing of this is also shown in FIG. 2.
- the refresh controller 20 generates refresh requests periodically so as to make sure that the memory array 10 is refreshed properly. Since the memory array 10 is refreshed one row of cells at a time, for a refresh time of 16ms, the refresh controller 20 generates one refresh request every 8 ⁇ s.
- the refresh request signal RREQ# is activated when there is a pending refresh. The activation of the RREQ# signal is detected by the arbiter 26 at the rising-edge of the MCLK signal. If no external access request is detected, the arbiter 26 drives both the Refresh Acknowledge RFACK# and ASEL signals low for one clock cycle. The former signals that the current memory cycle is used for refresh and the later selects the Refresh address from the refresh controller 20 as the address to the memory array 10.
- FIG. 3 shows a block diagram of the refresh controller 20, which includes a refresh address counter 40, a refresh timer 44 and a refresh accumulator 50.
- the refresh counter 40 provides the 11-bit row address to the memory array 10 during a refresh cycle.
- the refresh counter 40 is incremented at the end of the refresh cycle signaled by the deactivation of the refresh acknowledge RFACK#.
- the refresh timer 44 is reset (by the Reset signal) at power up.
- Timer 44 includes 12-bit counter 46 which provides a total count of 4095 cycles and a 12-input NAND gate 48. For a clock frequency of 100MHz, the timer 44 times up (signals Q0-Q11 are high) approximately every 8 ⁇ s.
- the refresh up RFUP# signal is driven low by NAND gate 48 for one clock cycle.
- This signal is input to the refresh accumulator 50 for incrementing its 3-bit up/down counter 52.
- the up/down counter 52 increments by one when RFUP# is driven low and decrements by one when RFACK# is driven low for one clock cycle.
- the counter 52 stops incrementing when it reaches the full count, that is when AQ0-AQ2 are all high. If the accumulator 50 count is not empty, that is signals AQ0-AQ2 are not equal to 000, Refresh Request RREQ# is asserted low by OR gate 54.
- the function of the accumulator 50 is illustrated as follows.
- the refresh requests are accumulated in the accumulator 50.
- the refresh request RREQ# signal to the arbiter 26 will continue to be asserted low until the accumulator 50 is empty.
- the accumulator 50 can accumulate up to 7 refreshes. This allows the system to continue external accesses for a period of up to 56 ⁇ s without losing refresh cycles.
- back-to-back external accesses longer than 56 ⁇ s in general do not occur.
- the counter 52 size can be increased or decreased to meet the application requirement.
- the signal MCLK which synchronizes the operations of the memory system is derived conventionally from the external clock signal CLK.
- MCLK can be generated by a conventional on-chip oscillator and PLL (phase locked loop). The PLL synchronizes the MCLK rising-edge to the output of the address transition detector which generates a pulse on the occurrence of a transition on the address bus.
- FIG. 4 shows an example of internal structure of arbiter 26 of FIG. 1, including in this embodiment a NAND gate 56 coupled as shown to inverter 58; thus refresh is prevented except in the absence of a pending memory array external access.
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- Engineering & Computer Science (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Computer Hardware Design (AREA)
- Dram (AREA)
- Semiconductor Memories (AREA)
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US37396 | 1998-03-09 | ||
US09/037,396 US6028804A (en) | 1998-03-09 | 1998-03-09 | Method and apparatus for 1-T SRAM compatible memory |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0942430A1 EP0942430A1 (en) | 1999-09-15 |
EP0942430B1 true EP0942430B1 (en) | 2006-08-23 |
Family
ID=21894121
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP99301728A Expired - Lifetime EP0942430B1 (en) | 1998-03-09 | 1999-03-08 | Method and apparatus for 1-T SRAM compatible memory |
Country Status (5)
Country | Link |
---|---|
US (1) | US6028804A (ja) |
EP (1) | EP0942430B1 (ja) |
JP (1) | JPH11297067A (ja) |
DE (1) | DE69932875T2 (ja) |
TW (1) | TW434545B (ja) |
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US6707743B2 (en) * | 1998-10-01 | 2004-03-16 | Monolithic System Technology, Inc. | Method and apparatus for completely hiding refresh operations in a DRAM device using multiple clock division |
US6504780B2 (en) * | 1998-10-01 | 2003-01-07 | Monolithic System Technology, Inc. | Method and apparatus for completely hiding refresh operations in a dram device using clock division |
US6496437B2 (en) | 1999-01-20 | 2002-12-17 | Monolithic Systems Technology, Inc. | Method and apparatus for forcing idle cycles to enable refresh operations in a semiconductor memory |
JP4339995B2 (ja) | 1999-11-16 | 2009-10-07 | パナソニック株式会社 | 半導体記憶装置 |
TW535161B (en) * | 1999-12-03 | 2003-06-01 | Nec Electronics Corp | Semiconductor memory device and its testing method |
US6941415B1 (en) * | 2000-08-21 | 2005-09-06 | Micron Technology, Inc. | DRAM with hidden refresh |
JP3726660B2 (ja) | 2000-09-01 | 2005-12-14 | セイコーエプソン株式会社 | 半導体メモリ装置のリフレッシュ制御 |
JP3726661B2 (ja) | 2000-09-01 | 2005-12-14 | セイコーエプソン株式会社 | 半導体メモリ装置のリフレッシュ制御 |
US6697909B1 (en) * | 2000-09-12 | 2004-02-24 | International Business Machines Corporation | Method and apparatus for performing data access and refresh operations in different sub-arrays of a DRAM cache memory |
JP3627647B2 (ja) | 2000-10-27 | 2005-03-09 | セイコーエプソン株式会社 | 半導体メモリ装置内のワード線の活性化 |
JP3705113B2 (ja) | 2000-10-27 | 2005-10-12 | セイコーエプソン株式会社 | 半導体メモリ装置内のワード線の活性化 |
JP3531602B2 (ja) | 2000-11-08 | 2004-05-31 | セイコーエプソン株式会社 | 半導体メモリ装置内のワード線の活性化 |
JP3967559B2 (ja) * | 2001-04-06 | 2007-08-29 | 富士通株式会社 | 制御回路及び半導体記憶装置 |
JP2002313079A (ja) | 2001-04-18 | 2002-10-25 | Seiko Epson Corp | 半導体メモリ装置の電源ノイズの抑制化 |
KR100394322B1 (ko) * | 2001-05-19 | 2003-08-09 | (주)이엠엘에스아이 | 리프레쉬 동작을 제어할 수 있는 디램 셀을 이용한 에스램호환 메모리 장치 |
KR100394587B1 (ko) * | 2001-05-19 | 2003-08-14 | (주)실리콘세븐 | 디램 셀을 이용한 에스램 호환 메모리 장치의 리프레쉬 회로 |
KR100401235B1 (ko) * | 2001-05-22 | 2003-10-17 | (주)실리콘세븐 | 디램 셀을 이용한 에스램 호환 메모리 장치의 로우 제어회로 |
JP4743999B2 (ja) * | 2001-05-28 | 2011-08-10 | ルネサスエレクトロニクス株式会社 | 半導体記憶装置 |
JP3985889B2 (ja) | 2001-08-08 | 2007-10-03 | 株式会社ルネサステクノロジ | 半導体装置 |
TW533413B (en) * | 2001-10-11 | 2003-05-21 | Cascade Semiconductor Corp | Asynchronous hidden refresh of semiconductor memory |
US6625077B2 (en) * | 2001-10-11 | 2003-09-23 | Cascade Semiconductor Corporation | Asynchronous hidden refresh of semiconductor memory |
US6643732B1 (en) | 2001-11-14 | 2003-11-04 | Etron Technology, Inc. | Delayed read/write scheme for SRAM interface compatible DRAM |
US6735139B2 (en) * | 2001-12-14 | 2004-05-11 | Silicon Storage Technology, Inc. | System and method for providing asynchronous SRAM functionality with a DRAM array |
JP2003196977A (ja) * | 2001-12-27 | 2003-07-11 | Fujitsu Ltd | 半導体記憶装置のデータアクセス方法、及び半導体記憶装置 |
US6638813B1 (en) | 2002-01-29 | 2003-10-28 | Taiwan Semiconductor Manufacturing Company | Method of forming a composite spacer to eliminate polysilicon stringers between elements in a pseudo SRAM cell |
JP4078119B2 (ja) * | 2002-04-15 | 2008-04-23 | 富士通株式会社 | 半導体メモリ |
KR100481819B1 (ko) * | 2002-08-27 | 2005-04-11 | (주)실리콘세븐 | 디램 셀을 사용하며, 칩 디스에이블 구간 중에 발생하는신호에 의하여 리프레쉬가 수행되도록 제어되는 동기식에스램 호한 메모리 |
US6795364B1 (en) * | 2003-02-28 | 2004-09-21 | Monolithic System Technology, Inc. | Method and apparatus for lengthening the data-retention time of a DRAM device in standby mode |
JP3705276B2 (ja) | 2003-04-21 | 2005-10-12 | セイコーエプソン株式会社 | 半導体メモリ装置におけるリフレッシュ制御および内部電圧の生成 |
KR100525459B1 (ko) * | 2003-05-16 | 2005-10-31 | (주)실리콘세븐 | 인출과 기입 동작 구간이 분리되는 리프레쉬 동작을수행하는 에스램 호환 메모리 및 그 구동방법 |
US20050229959A1 (en) * | 2004-04-16 | 2005-10-20 | Chen-Hsiung Lin | Sunshade structure |
US7113439B2 (en) * | 2004-04-22 | 2006-09-26 | Memocom Corp. | Refresh methods for RAM cells featuring high speed access |
US7433996B2 (en) * | 2004-07-01 | 2008-10-07 | Memocom Corp. | System and method for refreshing random access memory cells |
US7532532B2 (en) * | 2005-05-31 | 2009-05-12 | Micron Technology, Inc. | System and method for hidden-refresh rate modification |
US7274618B2 (en) * | 2005-06-24 | 2007-09-25 | Monolithic System Technology, Inc. | Word line driver for DRAM embedded in a logic process |
US7499307B2 (en) * | 2005-06-24 | 2009-03-03 | Mosys, Inc. | Scalable embedded DRAM array |
US7533222B2 (en) * | 2006-06-29 | 2009-05-12 | Mosys, Inc. | Dual-port SRAM memory using single-port memory cell |
KR20170025896A (ko) * | 2015-08-31 | 2017-03-08 | 에스케이하이닉스 주식회사 | 반도체 장치 및 이를 포함하는 반도체 시스템 |
US10394719B2 (en) | 2017-01-25 | 2019-08-27 | Samsung Electronics Co., Ltd. | Refresh aware replacement policy for volatile memory cache |
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JPS58155596A (ja) * | 1982-03-10 | 1983-09-16 | Hitachi Ltd | ダイナミツク型mosram |
US4625301A (en) * | 1983-11-30 | 1986-11-25 | Tandy Corporation | Dynamic memory refresh circuit |
US5617551A (en) * | 1992-09-18 | 1997-04-01 | New Media Corporation | Controller for refreshing a PSRAM using individual automatic refresh cycles |
JP3026474B2 (ja) * | 1993-04-07 | 2000-03-27 | 株式会社東芝 | 半導体集積回路 |
KR950014089B1 (ko) * | 1993-11-08 | 1995-11-21 | 현대전자산업주식회사 | 동기식 디램의 히든 셀프 리프레쉬 방법 및 장치 |
JP3165585B2 (ja) * | 1994-05-13 | 2001-05-14 | シャープ株式会社 | 情報処理装置 |
-
1998
- 1998-03-09 US US09/037,396 patent/US6028804A/en not_active Expired - Lifetime
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1999
- 1999-02-23 TW TW088102687A patent/TW434545B/zh not_active IP Right Cessation
- 1999-03-08 EP EP99301728A patent/EP0942430B1/en not_active Expired - Lifetime
- 1999-03-08 DE DE69932875T patent/DE69932875T2/de not_active Expired - Lifetime
- 1999-03-09 JP JP11061012A patent/JPH11297067A/ja active Pending
Also Published As
Publication number | Publication date |
---|---|
TW434545B (en) | 2001-05-16 |
US6028804A (en) | 2000-02-22 |
DE69932875D1 (de) | 2006-10-05 |
JPH11297067A (ja) | 1999-10-29 |
DE69932875T2 (de) | 2006-12-21 |
EP0942430A1 (en) | 1999-09-15 |
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